Sedimentary Structures and Waterway Sediments

Dr. Ahmad Redaa

2025-02-02

Sedimentary Structures

1. Bedding or Stratification

Source: Steven, E. (2015)

2. Graded Bedding

Source: https://epod.usra.edu

3. Cross Bedding

Source: Steven, E. (2015)

Source: Steven, E. (2015)

4. Ripple Marks

Source: https://blogs.egu.eu

5. Mud Cracks

Source: Steven, E. (2015)

Sediment Accumulation by Waterways

1. Stream Sediments

Depositional Features:

Significance:

2. Braided Stream Deposits

Source: https://www.coolgeography.co.uk

3. Floodplain Sediments

Source: https://www.coolgeography.co.uk

Depositional Features:

Significance:

4. Delta and Alluvial Fan Sediments

Source: https://abhipedia.abhimanu.com

Delta Deposits

Alluvial Fan Deposits

Significance:

Delta vs Alluvial Fan

Feature Delta Deposits Alluvial Fan Deposits
Location Found at river mouths where a river meets a standing body of water (lake, sea, or ocean). Found at the base of mountains or highlands where streams lose energy and deposit sediments on land.
Shape Triangular or lobate shape extending into the water (fan or bird-foot shape). Fan-shaped deposits spreading out from a central point, usually on land.
Sediment Size & Features Finer sediments (silt, clay, fine sand) due to prolonged transport and deposition in low-energy environments. May show layering and cross-bedding. Coarser sediments (gravel, sand, pebbles) due to short transport distances and high-energy environments. Often poorly sorted.
Flow Dynamics Dominated by relatively low-energy flow with distributary channels, sediment settling due to reduced velocity. High-energy, episodic flow with sudden deposition due to a rapid loss of velocity as water spreads out from a confined channel.

Summary